Argentina goalkeeper Sergio Romero's performances at the tournament have gone under the radar.

Three matches into Argentina's World Cup campaign, it would be easy to list their star men so far with reference to just one name: Lionel Messi. That would be to do a disservice to at least one man who is similarly undroppable, though. The performances of Sergio Romero in goal have, like Messi's in attack, not been of flawless brilliance but just as vital.

In Argentina's opening match against Bosnia-Herzegovina, he kept out five decent chances before letting in a late consolation in a 2-1 victory. In their final group game, the 3-2 win against Nigeria, he was a little less impressive, it's true -- particularly for Nigeria's second goal -- but there was very little he could do about their first and he otherwise didn't have a lot of work to do.

The match in between those two, though, was when many of Romero's detractors back home began to realise that, just maybe, they've got a better custodian between the sticks than they previously thought. When the squad was announced, most already knew Willy Caballero wouldn't be called up, Alejandro Sabella having constantly reaffirmed his faith in Romero, but disquiet about Romero remained.

It's not hard to understand why; though he's a good goalkeeper (with only one season in which he let in significantly more than a goal a game from a seven-year-long career in Europe) Romero has barely featured for Monaco since moving to the principality club for the 2013-14 season. Just three league appearances and then six in a run to the Coupe de France semifinals saw plenty of nerves surface surrounding his lack of playing time.

Caballero's performances for Málaga didn't help Romero's case in the public eye, but Sabella has been consistent with his squad selection ever since he took charge. He sees Romero as a dependable goalkeeper, as well as being a key member of the group of friends who make up Argentina's squad. It's often said that proponents of Totaalvoetbal wanted their goalkeepers to be as good with the ball at their feet as stopping shots. For Sabella, Romero's role in Argentina's group dynamic is just as crucial.

Sabella has been rewarded with decent performances and not only at this World Cup, either. In spite of doubts at the back, Argentina finished with the second best defensive record in South American qualifying (only Colombia conceded fewer), and it's difficult to remember any Romero howlers other than him being at fault for one of Paraguay's goals in a 5-2 Argentina win in Asunción close to end of the qualifying campaign.

With plenty of time to think over such rare errors while sitting on the Monaco bench, Romero clearly feels he has a point to prove at this World Cup. His performances so far have drawn the praise of his teammates, Atlético Madrid's Argentine manager Diego Simeone and even Rihanna, who's been responsible for some of the more idiosyncratic Twitter commentary during this tournament.

On Tuesday, Argentina take on Switzerland in their first knockout match and as Romero puts it: "From this point on, the margin for error is almost nonexistent."

He knows what's expected of him and his teammates know they can trust him. Against Xherdan Shaqiri and co, he'll have another chance to continue showing his bosses back at Monaco that he's no mug.